Such cells are described in my earlier U.S. Pat. Nos. 4,968,396 and 5,154,807, which have been found admirably to reduce exhaust by-products and improve fuel efficiency, as therein described in detail. While such cells have been found useful in vehicle and other diesel engines, as well as gasoline engines, the current direction of fuel refiners in changing the fuel chemistry, hopefully to improve the reduction of undesired by-products in the exhaust and/or improved mileage, and further experience particularly with diesel fuel operations, have now led to the discovery of significant improvements in cell construction. It is, accordingly, to such improved electrolytic-catalytic-electrochemical series potential cells, including optimum selection of fuel-reacting cell metals, particularly though not exclusively, for diesel fuel operation, that the present invention is directed.